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Anaesthesia for vascular surgery on extremities
VASCULAR ANAESTHESIA
Anaesthesia for vascular surgery on extremities
Learning objectives After reading this article, you should be able to:
Lawrence Caldicott
C
Catherine Farrow C
Abstract Patients presenting for peripheral vascular surgery often have multiple comorbidities due to the widespread nature of atherosclerotic disease. Diabetes is also very common. Cardiac events are the major cause of perioperative mortality. Preoperatively, any medical conditions should be optimized and consideration given to starting a b-blocker, if this is indicated. Surgery can be performed under general or regional anaesthesia, and there are potential pros and cons of each technique but no significant differences in outcome between the two methods. Patients are often anticoagulated pre- and perioperatively and an understanding of the implications of this to anaesthetic technique is vital. Peripheral arterial reconstruction or bypass surgery can be prolonged. Maintenance of normothermia is important, but significant fluid shifts and blood loss are relatively rare and invasive monitoring is not usually needed. Patients presenting for limb amputations are a high-risk group and have a high mortality and reduced long-term survival. Optimum preoperative and postoperative is especially important in this group to hopefully minimize the development of phantom limb pain, although no one particular anaesthetic technique has been shown to be consistently effective.
C
understand that patients presenting for lower limb revascularization have multiple comorbidities requiring thorough preoperative cardiac assessment consider the relative risks of general anaesthesia (GA) versus regional anaesthesia (RA) for lower limb revascularization procedures describe the management of patients presenting for amputation.
significant at around 5%. Perioperative morbidity is common and is primarily cardiac in origin. Preoperative management: medical therapy of existing medical conditions should be optimized preoperatively. Guidelines on the starting of b-blockers preoperatively have recently been updated,1 and in peripheral vascular surgery it is reasonable to consider starting b-blocker therapy if there is prior evidence of ischaemic heart disease, heart failure, cerebrovascular disease, diabetes mellitus, or renal insufficiency. This should be started well in advance of surgery and slowly titrated to blood pressure and heart rate changes. Preoperative assessment may include non-invasive cardiac testing as patients with PVD may be unable to exercise, thus masking cardiac symptoms. Cardiopulmonary exercise testing, (CPX) is becoming more popular and it may be worth considering, even in claudicants, as a significant proportion of them will be able to exercise on a bike and worthwhile results may be obtained.
Keywords Amputation; embolectomy; peripheral vascular disease
Lower limb surgery Revascularization procedures Early symptoms of lower limb ischaemia include intermittent claudication, progressing to critical ischaemia with rest pain and tissue loss. Atherosclerosis is a disease of the entire arterial tree and patients with peripheral vascular disease (PVD) have a high incidence of coronary, cerebral and renal vascular lesions resulting in a significant annual mortality rate. Medical treatment of lower limb ischaemia includes smoking cessation, control of diabetes, hypertension and cholesterol, exercise programmes and treatment with antiplatelet drugs. Surgical revascularization of the lower limb involves bypass of the diseased arterial segment with either synthetic tube grafts or autologous vein. More recently, arterial angioplasty (with or without stenting) has replaced the need for surgery in some cases (Figure 1). Given the prevalence of multiple comorbidities it is not surprising that perioperative mortality in elective surgery is
Angiogram of an atherosclerotic femoral artery before and after angioplasty. a Preprocedure, the irregular, narrowed arterial lumen can be seen with numerous collateral vessels. b Postprocedure, the artery has been widened and flow restored.
Lawrence Caldicott MB BS FRCA is a Consultant Anaesthetist at St James’s University Hospital, Leeds, UK. Conflicts of interest: none declared. Catherine Farrow MB BS FRCA is a Specialist Registrar in Anaesthesia at Leeds General Infirmary, Leeds, UK. Conflicts of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
Figure 1
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
Advantages and disadvantages of general and regional anaesthesia General anaesthesia
Regional anaesthesia Advantages Patient self-monitoring for cardiovascular and respiratory problems C Postoperative analgesia C Improved graft blood flow and tissue perfusion with possible reduced reoperation rate C Attenuation of surgical stress response C Reduced incidence of deep vein thrombosis
Advantages C Easier perioperative cardiovascular control C No patient discomfort during long procedures C More reliable
C
Disadvantages Postoperative problems including cardiovascular instability, unpredictable analgesic requirements, nausea and vomiting C Postoperative respiratory complications C Hypercoaguable state postoperatively
Disadvantages Technical difficulties in performing regional anaesthesia C Difficult to use alone in long procedures C Procedural risks including failure, inadequacy and complications C Risks associated with the concomitant use of anticoagulants and epidural haematoma formation
C
C
Table 1
Anaesthetic technique: the main aims of anaesthesia for lower limb revascularization are to ensure haemodynamic stability, normothermia, normovolaemia and good postoperative pain control. There appears to be no difference in mortality or cardiovascular morbidity between general and regional anaesthesia. The advantages and disadvantages of each technique are shown in Table 1. Duration of the surgical procedure and any need for arm vein grafts will influence choice of anaesthetic technique.
outweigh the potential anaesthetic benefits of a regional technique. Anaesthetists should be aware of a number of newer anticoagulant drugs in use.3 Intraoperative management: in addition to standard monitoring, the following also need to be considered. Cardiovascular: five-lead electrocardiography (ECG) or a CM5 three-lead configuration can be used to detect rhythm and ST segment changes more reliably. At lease one large-bore
General anaesthesia: induction of and emergence from anaesthesia should be as smooth as possible to maintain cardiovascular stability. Due to the prolonged nature of many peripheral revascularization procedures, there is usually a preference for intubation and controlled ventilation. Longer-acting opioids may be used for analgesia during maintenance and into the postoperative period although analgesia may also be achieved by use of a regional technique if there are no contraindications.
Guidelines for timing of perioperative neuraxial anaesthesia (RA) in patients taking anticoagulant drugs3 Anticoagulant drug Aspirin/non-steroidal anti-inflammatory drugs (NSAIDs) Clopidogrel Warfarin
Regional anaesthesia: RA produces sympathetic blockade which may improve graft flow and reduces thrombotic tendency. However, hypotension resulting from RA will adversely affect graft flow, and although RA may be associated with lower reoperation rates the evidence is conflicting. It may however be prudent to use RA in cases where there is a high risk of graft failure, such as distal revascularization procedures, or in patients with a previous failed bypass.2 RA can be used alone or in combination with sedation or GA. The use of an epidural will be more appropriate than spinal anaesthesia for prolonged operations. The timing of safe RA in relation to anticoagulant drug administration is essential to minimize the risk of epidural haematoma (Table 2). More vascular patients are now taking clopidogrel, particularly following coronary stenting, and this must be stopped at least 7 days before a regional anaesthetic technique. The risk of clotting of a coronary stent if clopidogrel is stopped preoperatively is high, and depends on the type of stent and the time from placement of the stent. The risks of myocardial infarction and death are high in these patients and usually far
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
Low-molecular weight heparin (LMWH) Unfractionated heparin
Thrombolysis
Proceed as normal, be aware of drug interactions Discontinue 7 days prior to RA International normalized ratio (INR) <1.5 for RA/removal of epidural catheter Allow 12 hours from dose before RA/removal of epidural catheter If high-dose LMWH used allow 24 hours before RA Allow 4 hours from dose before RA/removal of epidural catheter Intraoperatively delay intravenous bolus for at least 1 hour after RA Wait 2e4 hours from RA before subsequent dose Avoid RA except in extreme circumstances. Allow 10 days from dose before RA
Table 2
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
venous cannula is usually sited, but significant blood loss is unusual. Invasive blood pressure measurement with an arterial catheter is common, but a central venous catheter is not normally required unless the need for inotropic therapy or accurate fluid balance is anticipated. Cardiac output monitoring may be required for patients with poor left ventricular function or severe valvular disease.
administrating vasopressors, such as metaraminol, phenylephrine or ephedrine. Use of RA may reduce the severity of cardiovascular instability following reperfusion. There is also a transient drop in arterial oxygen saturation and a rise in end tidal CO2, as the ischaemic tissues are reperfused and the products of anaerobic respiration are ‘flushed out’. This effect is transient, lasting 5e10 minutes, usually requires no treatment and is evidence of successful reperfusion. Reperfusion is also often associated with a small drop in core temperature as the ischaemic limb is often quite cold.
Temperature: hypothermia can be detrimental, causing vasoconstriction, increased oxygen demand, increased blood viscosity and impaired haemostasis. Core temperature should therefore be monitored to ensure maintenance of normothermia, and active measures taken to minimize heat loss during these potentially long operations. These include ensuring adequate theatre air temperature, a warming mattress under the patient, warming intravenous fluids and blood products and using forced-air warming blankets These devices should not be used over body areas with poor or absent arterial blood supply, for example distal to cross-clamping.
Acute limb ischaemia Acute limb ischaemia (ALI) classically presents with pain, pallor, pulselessness, paraesthesia and paralysis and is an acute surgical emergency. Whilst it occurs most commonly in the leg it is occasionally seen in the arms. The cause in patients with preexisting PVD is usually thrombosis, but embolism also occurs and is strongly associated with atrial fibrillation. Overall mortality in this group of patients is high. A clinical classification of ALI (Table 3) allows rapid triage and appropriate treatment.
Renal: catheterization and hourly urine output measurement will reflect renal perfusion and function and are essential for patients with renal impairment.
Anaesthetic considerations: given the acute nature of a patient’s presentation, time for preoperative assessment and optimization is limited. The patient should be brought to theatre as quickly as possible and the anaesthetist should be closely involved in preoperative resuscitation. Infiltration of local anaesthetic by the surgeon will facilitate femoral arteriotomy and embolectomy in a cooperative patient. However general anaesthesia may be required for unsuccessful embolectomy, or if more extensive surgery is necessary, and will usually require invasive cardiovascular monitoring as previously described. Regional anaesthesia is likely to be contraindicated as almost all of these patients will have received anticoagulants prior to theatre. Perioperative cardiovascular instability following reperfusion may be severe in ALI compared to chronic limb ischaemia as there will be minimal collateral circulation. Tissue swelling and compartment syndrome (CS) are also possible after reperfusion, especially if the ischaemic time has been prolonged. The signs and symptoms of CS can be unreliable so direct pressure measurement of the compartments of the leg should be performed if there is swelling, pain or any doubt. Pressures greater than 30 mmHg, or if diastolic pressure is less than 30 mmHg above the compartment pressure, should be an indication for fasciotomies. If significant muscle necrosis is suspected myoglobinuria should be looked for and creatine kinase levels measured as this is the most sensitive test for rhabdomyolysis. If myoglobinuria is present measures should be taken to ensure a brisk diuresis to avoid renal failure.
Vein harvesting: veins are harvested for graft formation from the same or the contralateral leg unless previous surgery necessitates the use of arm veins. In this situation the operative arm should thus be avoided for intravenous access and monitoring and will also dictate the need for GA. Radial arterial lines are useful in patients in whom both arms and both legs are being used for vein harvesting, and a central line may be needed purely for venous access in these patients. Anticoagulation: intravenous heparin is given before clamping of the arterial supply to the limb, usually 5000 IU for a normal-sized adult patient. Coagulation monitoring is not usually required, but activated clotting time is easily measured in the operating theatre. Reversal with protamine is not normally required. Fluid management: crystalloids and colloids are used to replace preoperative dehydration and surgical losses. Haemoglobin and haematocrit estimations can indicate need for blood transfusion, which is however quite uncommon. Reperfusion: cardiovascular changes following clamp release occur as a result of decreased systemic vascular resistance and venous return. The fall in blood pressure can be minimized by ensuring normovolaemia prior to clamp release, decreasing clamp time, sequential release of each major arterial branch and
Classification and management of acute limb ischaemia Classification I Viable (non-threatened) II Threatened III Irreversible
Clinical features Sensory change None Rest pain Anaesthetic
Motor change None Moderate Paralysis
Audible doppler signals Yes Venous only No
Management Heparin Angiogram Yes Elective Yes Urgent Yes No
Treatment Elective revascularization Urgent revascularization Delayed amputation
Table 3
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
Amputation Amputation may be a primary procedure for overwhelming infection or intractable pain, or secondary to failed revascularization surgery. Underlying medical conditions, especially diabetes, are common, and together with the necrotic tissue and infection make these patients amongst the sickest of vascular patients. This group is at high risk for perioperative morbidity and death, and has a reduced long-term survival.
Anaesthetic considerations: vascular access should be sited in the non-operative arm and should include a wide-bore cannula. Rib resection can be very painful postoperatively, commonly requiring the use of opiates in the form of patient-controlled analgesia systems. Superficial cervical plexus block may be a useful adjunct, especially as many of these patients may suffer with chronic pain and already be receiving a multitude of analgesics. Thorascopic thoracic sympathectomy This is performed for palmar hyperhidrosis and involves collapse of the lung and division of the thoracic sympathetic trunk between T2 and T5 through small incisions in the chest wall and using a video-assisted thorascopic technique. Patients are usually young and fit and treatment has a high success rate. Complications of surgery are rare but include pneumothorax, haemothorax, damage to chest structures, commonly intercostal arteries, Horner’s syndrome, prolonged postoperative pain often perceived as ‘back pain’ and compensatory hyperhidrosis elsewhere on the body.
Phantom limb pain (PLP): PLP is a continuing perception of pain from the limb following amputation and occurs in up to 70% at some time, but can persist in a severe form. It is highly resistant to conventional analgesics. Preoperative analgesia is important as many of these patients have chronic severe ischaemic pain causing dorsal horn sensitization in the spinal cord and leading to a high likelihood of subsequent phantom limb pain. Paracetamol, morphine, anti-depressants, anticonvulsants, ketamine and gabapentin may all need to be used. Perioperatively epidural insertion provides good analgesia, but the evidence that it reduces the incidence of phantom limb pain is poor. Neuroaxial blocks may be relatively contraindicated if there is evidence of sepsis or bacteraemia. Postoperatively, nerve blocks, morphine and ketamine infusions may all be needed. A perineural sciatic catheter may be placed next to the sciatic nerve stump under direct vision by the surgeon, and 2e3 ml/hour of 0.5% bupivicaine can be infused postoperatively to help reduce postoperative pain.
Anaesthetic considerations: preoperative investigations may include only a baseline chest radiograph. General anaesthesia is required and generally this is done using one-lung ventilation (OLV) via a double-lumen tube. Some centres now use single-lumen tubes or allow the patient to breathe spontaneously through a laryngeal mask airway (LMA) and rely on the insufflation of gas into the pleural space to cause adequate lung collapse. Tracheal intubation is less likely to cause hypoxia than OLV, but gives less clear surgical access. Carbon dioxide insufflation requires close co-operation between surgeon and anaesthetist with an insufflation pressure limit set to prevent excess intrathoracic pressure or volume. This can cause physiological changes consistent with a tension pneumothorax (hypotension, hypoxia, bradycardia), but can be immediately reversed by removal of gas from the chest cavity. Cardiac complications aside from those described above are rare, but include cardiac arrhythmias from denervation of T2eT4 sympathetic ganglia. Hypoxia occurs mainly as a result of OLV. At the end of the procedure the lung must be fully re-expanded under direct vision of the thoracoscope and a postoperative chest radiograph performed. Bilateral procedures involving sequential collapse and inflation of the lungs are possible.
Varicose vein surgery The majority of surgery is usually performed as a daycase in younger patients for symptoms such as pain, swelling, itching, or for cosmetic reasons. Procedures, which can be bilateral, include saphenofemoral junction ligation with stripping of the long saphenous vein, and saphenopopliteal junction ligation which will require the patient to be in the lateral or prone position. The main operation may be combined with multiple avulsions to remove varicosities which can bleed profusely. Whilst significant blood loss is rare there is that potential which can be minimized by elevating the legs during the procedure.
Upper limb surgery
A-V fistula formation/revision Patients requiring arteriovenous fistula surgery to allow dialysis commonly have multiple comorbidities related to renal failure and are likely to have received recent dialysis. Preoperatively it is essential therefore to check plasma electrolyte levels. This surgery is commonly performed under local or regional anaesthesia. Ultrasound-guided supraclavicular or axillary block can be performed, although the former with caution in patients with respiratory disease as the subsequent diaphragmatic paralysis can cause respiratory compromise. A
Thoracic outlet syndrome (TOS) TOS results from compression of the subclavian vessels or brachial plexus between the clavicle, first rib and scalene muscles. Symptoms relate to either nerve compression (C8/T1 nerve root being most commonly affected) or vascular insufficiency. Surgical treatment is aimed at increasing the space available by resecting the first rib, and is reserved for severe cases, about 5% of sufferers.
REFERENCES 1 Fleischmann KE, Beckman JA, Buller CE, et al. 2009 ACCF/AHA focused update on perioperative beta blockade. A report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines. J Am Coll Cardiol 2009; 54: 13e118. doi:10.1016/j.jacc.2009.07.010.
Anaesthetic considerations: GA is usual and in patients requiring surgery in the supine position spontaneous respiration via a laryngeal mask airway is common. Intubation and intermittent positive pressure ventilation (IPPV) are required for prone positioning. Moderate amounts of analgesia only are required, for example short-acting opiates, and oral simple analgesics postoperatively supplemented with local anaesthetic (LA) infiltration of incisions.
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
2 Breen P, Park KW. General anesthesia versus regional anesthesia. Int Anesthesiol Clin 2002 Winter; 40: 61e71. 3 Horlocker TT, Wedel DJ, Benzon H, et al. Regional anesthesia in the anticoagulated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Reg Anesth Pain Med 2003; 28: 172e97.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
FURTHER READING Bannister J, Wildsmith JAW. Anaesthesia for vascular surgery. London: Arnold, 2000. Caldicott L, Lumb A, McCoy D. Vascular anaesthesia e a practical handbook. Oxford: Butterworth Heinemann, 1999. Kaplan JA, Lake CL, Murray MJ. Vascular anaesthesia. Philadelphia: Churchill Livingstone, 2004.
183
Ó 2010 Elsevier Ltd. All rights reserved.
Anaesthesia for vascular surgery on extremities
Learning objectives After reading this article, you should be able to:
Lawrence Caldicott
C
Catherine Farrow C
Abstract Patients presenting for peripheral vascular surgery often have multiple comorbidities due to the widespread nature of atherosclerotic disease. Diabetes is also very common. Cardiac events are the major cause of perioperative mortality. Preoperatively, any medical conditions should be optimized and consideration given to starting a b-blocker, if this is indicated. Surgery can be performed under general or regional anaesthesia, and there are potential pros and cons of each technique but no significant differences in outcome between the two methods. Patients are often anticoagulated pre- and perioperatively and an understanding of the implications of this to anaesthetic technique is vital. Peripheral arterial reconstruction or bypass surgery can be prolonged. Maintenance of normothermia is important, but significant fluid shifts and blood loss are relatively rare and invasive monitoring is not usually needed. Patients presenting for limb amputations are a high-risk group and have a high mortality and reduced long-term survival. Optimum preoperative and postoperative is especially important in this group to hopefully minimize the development of phantom limb pain, although no one particular anaesthetic technique has been shown to be consistently effective.
C
understand that patients presenting for lower limb revascularization have multiple comorbidities requiring thorough preoperative cardiac assessment consider the relative risks of general anaesthesia (GA) versus regional anaesthesia (RA) for lower limb revascularization procedures describe the management of patients presenting for amputation.
significant at around 5%. Perioperative morbidity is common and is primarily cardiac in origin. Preoperative management: medical therapy of existing medical conditions should be optimized preoperatively. Guidelines on the starting of b-blockers preoperatively have recently been updated,1 and in peripheral vascular surgery it is reasonable to consider starting b-blocker therapy if there is prior evidence of ischaemic heart disease, heart failure, cerebrovascular disease, diabetes mellitus, or renal insufficiency. This should be started well in advance of surgery and slowly titrated to blood pressure and heart rate changes. Preoperative assessment may include non-invasive cardiac testing as patients with PVD may be unable to exercise, thus masking cardiac symptoms. Cardiopulmonary exercise testing, (CPX) is becoming more popular and it may be worth considering, even in claudicants, as a significant proportion of them will be able to exercise on a bike and worthwhile results may be obtained.
Keywords Amputation; embolectomy; peripheral vascular disease
Lower limb surgery Revascularization procedures Early symptoms of lower limb ischaemia include intermittent claudication, progressing to critical ischaemia with rest pain and tissue loss. Atherosclerosis is a disease of the entire arterial tree and patients with peripheral vascular disease (PVD) have a high incidence of coronary, cerebral and renal vascular lesions resulting in a significant annual mortality rate. Medical treatment of lower limb ischaemia includes smoking cessation, control of diabetes, hypertension and cholesterol, exercise programmes and treatment with antiplatelet drugs. Surgical revascularization of the lower limb involves bypass of the diseased arterial segment with either synthetic tube grafts or autologous vein. More recently, arterial angioplasty (with or without stenting) has replaced the need for surgery in some cases (Figure 1). Given the prevalence of multiple comorbidities it is not surprising that perioperative mortality in elective surgery is
Angiogram of an atherosclerotic femoral artery before and after angioplasty. a Preprocedure, the irregular, narrowed arterial lumen can be seen with numerous collateral vessels. b Postprocedure, the artery has been widened and flow restored.
Lawrence Caldicott MB BS FRCA is a Consultant Anaesthetist at St James’s University Hospital, Leeds, UK. Conflicts of interest: none declared. Catherine Farrow MB BS FRCA is a Specialist Registrar in Anaesthesia at Leeds General Infirmary, Leeds, UK. Conflicts of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
Figure 1
179
Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
Advantages and disadvantages of general and regional anaesthesia General anaesthesia
Regional anaesthesia Advantages Patient self-monitoring for cardiovascular and respiratory problems C Postoperative analgesia C Improved graft blood flow and tissue perfusion with possible reduced reoperation rate C Attenuation of surgical stress response C Reduced incidence of deep vein thrombosis
Advantages C Easier perioperative cardiovascular control C No patient discomfort during long procedures C More reliable
C
Disadvantages Postoperative problems including cardiovascular instability, unpredictable analgesic requirements, nausea and vomiting C Postoperative respiratory complications C Hypercoaguable state postoperatively
Disadvantages Technical difficulties in performing regional anaesthesia C Difficult to use alone in long procedures C Procedural risks including failure, inadequacy and complications C Risks associated with the concomitant use of anticoagulants and epidural haematoma formation
C
C
Table 1
Anaesthetic technique: the main aims of anaesthesia for lower limb revascularization are to ensure haemodynamic stability, normothermia, normovolaemia and good postoperative pain control. There appears to be no difference in mortality or cardiovascular morbidity between general and regional anaesthesia. The advantages and disadvantages of each technique are shown in Table 1. Duration of the surgical procedure and any need for arm vein grafts will influence choice of anaesthetic technique.
outweigh the potential anaesthetic benefits of a regional technique. Anaesthetists should be aware of a number of newer anticoagulant drugs in use.3 Intraoperative management: in addition to standard monitoring, the following also need to be considered. Cardiovascular: five-lead electrocardiography (ECG) or a CM5 three-lead configuration can be used to detect rhythm and ST segment changes more reliably. At lease one large-bore
General anaesthesia: induction of and emergence from anaesthesia should be as smooth as possible to maintain cardiovascular stability. Due to the prolonged nature of many peripheral revascularization procedures, there is usually a preference for intubation and controlled ventilation. Longer-acting opioids may be used for analgesia during maintenance and into the postoperative period although analgesia may also be achieved by use of a regional technique if there are no contraindications.
Guidelines for timing of perioperative neuraxial anaesthesia (RA) in patients taking anticoagulant drugs3 Anticoagulant drug Aspirin/non-steroidal anti-inflammatory drugs (NSAIDs) Clopidogrel Warfarin
Regional anaesthesia: RA produces sympathetic blockade which may improve graft flow and reduces thrombotic tendency. However, hypotension resulting from RA will adversely affect graft flow, and although RA may be associated with lower reoperation rates the evidence is conflicting. It may however be prudent to use RA in cases where there is a high risk of graft failure, such as distal revascularization procedures, or in patients with a previous failed bypass.2 RA can be used alone or in combination with sedation or GA. The use of an epidural will be more appropriate than spinal anaesthesia for prolonged operations. The timing of safe RA in relation to anticoagulant drug administration is essential to minimize the risk of epidural haematoma (Table 2). More vascular patients are now taking clopidogrel, particularly following coronary stenting, and this must be stopped at least 7 days before a regional anaesthetic technique. The risk of clotting of a coronary stent if clopidogrel is stopped preoperatively is high, and depends on the type of stent and the time from placement of the stent. The risks of myocardial infarction and death are high in these patients and usually far
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
Low-molecular weight heparin (LMWH) Unfractionated heparin
Thrombolysis
Proceed as normal, be aware of drug interactions Discontinue 7 days prior to RA International normalized ratio (INR) <1.5 for RA/removal of epidural catheter Allow 12 hours from dose before RA/removal of epidural catheter If high-dose LMWH used allow 24 hours before RA Allow 4 hours from dose before RA/removal of epidural catheter Intraoperatively delay intravenous bolus for at least 1 hour after RA Wait 2e4 hours from RA before subsequent dose Avoid RA except in extreme circumstances. Allow 10 days from dose before RA
Table 2
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
venous cannula is usually sited, but significant blood loss is unusual. Invasive blood pressure measurement with an arterial catheter is common, but a central venous catheter is not normally required unless the need for inotropic therapy or accurate fluid balance is anticipated. Cardiac output monitoring may be required for patients with poor left ventricular function or severe valvular disease.
administrating vasopressors, such as metaraminol, phenylephrine or ephedrine. Use of RA may reduce the severity of cardiovascular instability following reperfusion. There is also a transient drop in arterial oxygen saturation and a rise in end tidal CO2, as the ischaemic tissues are reperfused and the products of anaerobic respiration are ‘flushed out’. This effect is transient, lasting 5e10 minutes, usually requires no treatment and is evidence of successful reperfusion. Reperfusion is also often associated with a small drop in core temperature as the ischaemic limb is often quite cold.
Temperature: hypothermia can be detrimental, causing vasoconstriction, increased oxygen demand, increased blood viscosity and impaired haemostasis. Core temperature should therefore be monitored to ensure maintenance of normothermia, and active measures taken to minimize heat loss during these potentially long operations. These include ensuring adequate theatre air temperature, a warming mattress under the patient, warming intravenous fluids and blood products and using forced-air warming blankets These devices should not be used over body areas with poor or absent arterial blood supply, for example distal to cross-clamping.
Acute limb ischaemia Acute limb ischaemia (ALI) classically presents with pain, pallor, pulselessness, paraesthesia and paralysis and is an acute surgical emergency. Whilst it occurs most commonly in the leg it is occasionally seen in the arms. The cause in patients with preexisting PVD is usually thrombosis, but embolism also occurs and is strongly associated with atrial fibrillation. Overall mortality in this group of patients is high. A clinical classification of ALI (Table 3) allows rapid triage and appropriate treatment.
Renal: catheterization and hourly urine output measurement will reflect renal perfusion and function and are essential for patients with renal impairment.
Anaesthetic considerations: given the acute nature of a patient’s presentation, time for preoperative assessment and optimization is limited. The patient should be brought to theatre as quickly as possible and the anaesthetist should be closely involved in preoperative resuscitation. Infiltration of local anaesthetic by the surgeon will facilitate femoral arteriotomy and embolectomy in a cooperative patient. However general anaesthesia may be required for unsuccessful embolectomy, or if more extensive surgery is necessary, and will usually require invasive cardiovascular monitoring as previously described. Regional anaesthesia is likely to be contraindicated as almost all of these patients will have received anticoagulants prior to theatre. Perioperative cardiovascular instability following reperfusion may be severe in ALI compared to chronic limb ischaemia as there will be minimal collateral circulation. Tissue swelling and compartment syndrome (CS) are also possible after reperfusion, especially if the ischaemic time has been prolonged. The signs and symptoms of CS can be unreliable so direct pressure measurement of the compartments of the leg should be performed if there is swelling, pain or any doubt. Pressures greater than 30 mmHg, or if diastolic pressure is less than 30 mmHg above the compartment pressure, should be an indication for fasciotomies. If significant muscle necrosis is suspected myoglobinuria should be looked for and creatine kinase levels measured as this is the most sensitive test for rhabdomyolysis. If myoglobinuria is present measures should be taken to ensure a brisk diuresis to avoid renal failure.
Vein harvesting: veins are harvested for graft formation from the same or the contralateral leg unless previous surgery necessitates the use of arm veins. In this situation the operative arm should thus be avoided for intravenous access and monitoring and will also dictate the need for GA. Radial arterial lines are useful in patients in whom both arms and both legs are being used for vein harvesting, and a central line may be needed purely for venous access in these patients. Anticoagulation: intravenous heparin is given before clamping of the arterial supply to the limb, usually 5000 IU for a normal-sized adult patient. Coagulation monitoring is not usually required, but activated clotting time is easily measured in the operating theatre. Reversal with protamine is not normally required. Fluid management: crystalloids and colloids are used to replace preoperative dehydration and surgical losses. Haemoglobin and haematocrit estimations can indicate need for blood transfusion, which is however quite uncommon. Reperfusion: cardiovascular changes following clamp release occur as a result of decreased systemic vascular resistance and venous return. The fall in blood pressure can be minimized by ensuring normovolaemia prior to clamp release, decreasing clamp time, sequential release of each major arterial branch and
Classification and management of acute limb ischaemia Classification I Viable (non-threatened) II Threatened III Irreversible
Clinical features Sensory change None Rest pain Anaesthetic
Motor change None Moderate Paralysis
Audible doppler signals Yes Venous only No
Management Heparin Angiogram Yes Elective Yes Urgent Yes No
Treatment Elective revascularization Urgent revascularization Delayed amputation
Table 3
ANAESTHESIA AND INTENSIVE CARE MEDICINE 11:5
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Ó 2010 Elsevier Ltd. All rights reserved.
VASCULAR ANAESTHESIA
Amputation Amputation may be a primary procedure for overwhelming infection or intractable pain, or secondary to failed revascularization surgery. Underlying medical conditions, especially diabetes, are common, and together with the necrotic tissue and infection make these patients amongst the sickest of vascular patients. This group is at high risk for perioperative morbidity and death, and has a reduced long-term survival.
Anaesthetic considerations: vascular access should be sited in the non-operative arm and should include a wide-bore cannula. Rib resection can be very painful postoperatively, commonly requiring the use of opiates in the form of patient-controlled analgesia systems. Superficial cervical plexus block may be a useful adjunct, especially as many of these patients may suffer with chronic pain and already be receiving a multitude of analgesics. Thorascopic thoracic sympathectomy This is performed for palmar hyperhidrosis and involves collapse of the lung and division of the thoracic sympathetic trunk between T2 and T5 through small incisions in the chest wall and using a video-assisted thorascopic technique. Patients are usually young and fit and treatment has a high success rate. Complications of surgery are rare but include pneumothorax, haemothorax, damage to chest structures, commonly intercostal arteries, Horner’s syndrome, prolonged postoperative pain often perceived as ‘back pain’ and compensatory hyperhidrosis elsewhere on the body.
Phantom limb pain (PLP): PLP is a continuing perception of pain from the limb following amputation and occurs in up to 70% at some time, but can persist in a severe form. It is highly resistant to conventional analgesics. Preoperative analgesia is important as many of these patients have chronic severe ischaemic pain causing dorsal horn sensitization in the spinal cord and leading to a high likelihood of subsequent phantom limb pain. Paracetamol, morphine, anti-depressants, anticonvulsants, ketamine and gabapentin may all need to be used. Perioperatively epidural insertion provides good analgesia, but the evidence that it reduces the incidence of phantom limb pain is poor. Neuroaxial blocks may be relatively contraindicated if there is evidence of sepsis or bacteraemia. Postoperatively, nerve blocks, morphine and ketamine infusions may all be needed. A perineural sciatic catheter may be placed next to the sciatic nerve stump under direct vision by the surgeon, and 2e3 ml/hour of 0.5% bupivicaine can be infused postoperatively to help reduce postoperative pain.
Anaesthetic considerations: preoperative investigations may include only a baseline chest radiograph. General anaesthesia is required and generally this is done using one-lung ventilation (OLV) via a double-lumen tube. Some centres now use single-lumen tubes or allow the patient to breathe spontaneously through a laryngeal mask airway (LMA) and rely on the insufflation of gas into the pleural space to cause adequate lung collapse. Tracheal intubation is less likely to cause hypoxia than OLV, but gives less clear surgical access. Carbon dioxide insufflation requires close co-operation between surgeon and anaesthetist with an insufflation pressure limit set to prevent excess intrathoracic pressure or volume. This can cause physiological changes consistent with a tension pneumothorax (hypotension, hypoxia, bradycardia), but can be immediately reversed by removal of gas from the chest cavity. Cardiac complications aside from those described above are rare, but include cardiac arrhythmias from denervation of T2eT4 sympathetic ganglia. Hypoxia occurs mainly as a result of OLV. At the end of the procedure the lung must be fully re-expanded under direct vision of the thoracoscope and a postoperative chest radiograph performed. Bilateral procedures involving sequential collapse and inflation of the lungs are possible.
Varicose vein surgery The majority of surgery is usually performed as a daycase in younger patients for symptoms such as pain, swelling, itching, or for cosmetic reasons. Procedures, which can be bilateral, include saphenofemoral junction ligation with stripping of the long saphenous vein, and saphenopopliteal junction ligation which will require the patient to be in the lateral or prone position. The main operation may be combined with multiple avulsions to remove varicosities which can bleed profusely. Whilst significant blood loss is rare there is that potential which can be minimized by elevating the legs during the procedure.
Upper limb surgery
A-V fistula formation/revision Patients requiring arteriovenous fistula surgery to allow dialysis commonly have multiple comorbidities related to renal failure and are likely to have received recent dialysis. Preoperatively it is essential therefore to check plasma electrolyte levels. This surgery is commonly performed under local or regional anaesthesia. Ultrasound-guided supraclavicular or axillary block can be performed, although the former with caution in patients with respiratory disease as the subsequent diaphragmatic paralysis can cause respiratory compromise. A
Thoracic outlet syndrome (TOS) TOS results from compression of the subclavian vessels or brachial plexus between the clavicle, first rib and scalene muscles. Symptoms relate to either nerve compression (C8/T1 nerve root being most commonly affected) or vascular insufficiency. Surgical treatment is aimed at increasing the space available by resecting the first rib, and is reserved for severe cases, about 5% of sufferers.
REFERENCES 1 Fleischmann KE, Beckman JA, Buller CE, et al. 2009 ACCF/AHA focused update on perioperative beta blockade. A report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines. J Am Coll Cardiol 2009; 54: 13e118. doi:10.1016/j.jacc.2009.07.010.
Anaesthetic considerations: GA is usual and in patients requiring surgery in the supine position spontaneous respiration via a laryngeal mask airway is common. Intubation and intermittent positive pressure ventilation (IPPV) are required for prone positioning. Moderate amounts of analgesia only are required, for example short-acting opiates, and oral simple analgesics postoperatively supplemented with local anaesthetic (LA) infiltration of incisions.
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2 Breen P, Park KW. General anesthesia versus regional anesthesia. Int Anesthesiol Clin 2002 Winter; 40: 61e71. 3 Horlocker TT, Wedel DJ, Benzon H, et al. Regional anesthesia in the anticoagulated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Reg Anesth Pain Med 2003; 28: 172e97.
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FURTHER READING Bannister J, Wildsmith JAW. Anaesthesia for vascular surgery. London: Arnold, 2000. Caldicott L, Lumb A, McCoy D. Vascular anaesthesia e a practical handbook. Oxford: Butterworth Heinemann, 1999. Kaplan JA, Lake CL, Murray MJ. Vascular anaesthesia. Philadelphia: Churchill Livingstone, 2004.
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